37 Park/Neutral Switch Failure - (P 1899)

37 PARK/NEUTRAL SWITCH FAILURE - (P 1899) (AUTOMATIC TRANSMISSIONS ONLY)





The Powertrain Control Module (PCM) sends out 9 volts from pin 50 to the park/neutral switch. If the switch is positioned in either park or neutral, the voltage is pulled to ground through the switch. If the park/neutral switch is positioned in any other gear, the circuit is opened. allowing the PCM to recognize the 9-volt signal. The diagnostics for the park/neutral switch are divided into two categories. The first is to identify if the park/neutral switch is indicating park or neutral while driving. The second is to identify a condition in which the vehicle is in park or neutral, while the PCM indicates drive or reverse. The conditions necessary to diagnose the first portion of the DTC are listed below.

ENABLING CONDITIONS
- Vehicle speed greater than 50 MPH
- Engine RPM between 1,984 and 4,480
- TPS voltage is greater than 0.49 volt above minimum TPS
- MAP is greater than 66% of barometric pressure

The Malfunction Indicator Lamp (MIL) is illuminated and the DTC is stored if the PCM recognizes low voltage at pin 50 for a period of ten seconds.

This malfunction could possibly be caused by problems with any of the following components:

- Park/neutral switch
- Wiring from PCM to the park/neutral switch (shorted to ground) PCM

The second portion of the test is listed below:

ENABLING CONDITIONS
- Vehicle must not be moving
- 15 or fewer crank edges recognized by the PCM (engine cranking)

The PCM recognizes a failed condition when the input at pin 50 indicates either drive or reverse while cranking. The MIL illuminates and a DTC is stored only after the failed condition is indicated and the engine has started.

This malfunction could possibly be caused by problems with any of the following components:

- Circuit between the PCM and the park/neutral switch (open)
- PCM